Two new bis-iridoids isolated from Scabiosa stellata and their antibacterial, antioxidant, anti-tyrosinase and cytotoxic activities

Abstract

This study presents the chemical profile investigation of a 70% ethanol extract obtained from Scabiosa stellata, a medicinal herbaceous traditionally used to treat heel cracks. A ¹³C NMR-based dereplication methodology was firstly applied on centrifugal partition chromatography-generated fractions in order to quickly identify the major compounds of the extract. The dereplication process was then completed by semi-preparative high-performance liquid chromatography in order to identify unknown or minor compounds. Two new bis-iridoids, namely 7-O-caffeoyl-sylvestroside I (1) and 7-O-(p-coumaroyl)-sylvestroside I (2), together with ten known compounds (3-12) were isolated. Their structures were elucidated by spectroscopic methods including NMR and HR-ESI-MS. The antibacterial, anti-tyrosinase and DPPH radical scavenging activities of the crude extract, fractions, and isolated compounds were evaluated. A significant antibacterial activity was observed for nine isolated compounds, particularly 1 and 2 which yielded MIC values of 31.2μg/mL against Enterococcus faecalis and 62.5μg/mL against Staphylococcus epidermidis. The cytotoxic activity of these new bis-iridoids was evaluated on a fibrosarcoma cell line (HT1080) and only compound 1 exhibited a moderate cytotoxic activity (IC₅₀ 35.9μg/mL).

Keywords: Antibacterial activity; Bis-iridoid glucoside; Caprifoliaceae; Cytotoxic activity; Dereplication; Scabiosa stellata.